- Star Tales - Caelum (ianridpath.com)
This small and insignificant constellation in the southern hemisphere, representing an engraver’s chisel, is one of the inventions of the 18th-century French astronomer Nicolas Louis de Lacaille. He introduced it on his map of the southern stars published in 1756, where he gave it the French name les Burins (although in the accompanying star catalogue it was listed as Burin, singular). On the second edition of the map in 1763 this was Latinized to Caelum Scalptorium. In 1844 the English astronomer John Herschel proposed shortening the name to Caelum. Francis Baily adopted this suggestion in his British Association Catalogue of 1845, and it has been known as Caelum ever since.
- Empty set (Wikipedia)
In mathematics, the empty set is the unique set having no elements; its size or cardinality (count of elements in a set) is zero. Some axiomatic set theories ensure that the empty set exists by including an axiom of empty set, while in other theories, its existence can be deduced. Many possible properties of sets are vacuously true for the empty set.